Query caching can really help boost Magento’s performance where common queries are being called often, especially with Magento’s sprawling data structure.
Check to see if Query Caching is available:
mysql> show variables like ‘have_query_cache’;
If query_cache_size is 0 then it is effectively off. To turn it on, set the value in bytes: (8MB is 1024*1024*8 = 8388608)
SET GLOBAL query_cache_size = 8388608;
It is also possible to set these values in the mysql config file:
query_cache_size = 268435456
These may already exist but be commented out.
Note that you can view all the of the query cache settings (handy for checking they are set) by running this:
mysql > show variables like ‘%query_cache%’;
If you have previously cached queries and you need to clear them then you can call:
RESET QUERY CACHE;
However, you will need to be have reload privileges, which users should not have, so will probably require you to go in as admin.